Pedal Spindle Extenders - precisely what I need. Thank you! (now, why aren't the supposedly knowledgeable staff at the bike shop aware of these?)
The seat, I agree, will be a tougher one. While I agree that I definitely need to build up some callous/rhinoceros skin where arse meets seat, I nonetheless will never find this seat in the least bit comfortable, and at the moment I am not at all fit enough to spend most of my time riding. It's great exercise, but I'd prefer that it not also be a test of my pain threshold's endurance to go riding for half an hour. Gel seemed like a brilliant idea when I first encountered it, but at the moment it seems not so hot - the giving nature of it, it seems to me, means that the hardest parts of the posterior, particularly on a heavy person, are going to end up getting the hardest parts of the seat, as the gel compresses. Maybe there's more to the physics of gel of which I am unaware, but my experience with it has nonetheless been uniformly bad.
Whatever the case, thanks again for the pointer to the extenders - they're perfect for my problem.